Now, thanks to a recent video she posted on Instagram, we know one of her go-to moves for building a super strong core and upper body. It’s a classic (yet tough as hell) variation of a plank, called a shoulder tap plank. You can check out the move in her Instagram video here:

“[Shoulder tap planks] are excellent because you have to stabilize your entire body while alternating your arms,” Borden tells SELF. “You get immediate feedback if your form is off because you can feel and see your hips moving.”

The move works practically every muscle group in your body, including your serratus anterior (the region around your rib cage that helps your core hold still), trapezius (a major muscle in your upper back and neck), triceps, glute medius (a hip adductor muscle on the outer side of the pelvis), obliques (muscles on both sides of your core) and erector spinae (a set of muscles in your lower back), NYC-based certified strength and conditioning specialist Mike Clancy tells SELF.

“It’s especially great for stabilizing multiple areas of your shoulder, including your rotator cuff and scapula [aka shoulder blade],” he adds. Having strong, stabilized shoulders is important for doing many movements in the gym (like bench presses and push-ups) as well as everyday life (like pulling a heavy suitcase out of an overhead compartment) effectively and safely.

“Your shoulder is the most mobile joint in the body, but also the most easily injured,” Clancy says. The more stabilized your scapula is, the less likely you are to injure it.

Shoulder tap planks are also a great single-arm exercise. By shifting all of your weight to one arm—even just for a moment—you force each arm and shoulder to do work without help from the other side.

“I love single-arm movements in general because they can help you spot weaknesses on either side,” Amanda Shannon Verrengia, Pittsburgh-based certified personal trainer and run coach, tells SELF.

Most of us are naturally stronger on one side (usually your dominant side), and single-arm moves can help correct these muscle imbalances. This is important because imbalances can lead to chronic pain and injury over time, if they’re glaring enough for you to notice and go uncorrected for too long. Single-arm moves (and unilateral exercises in general) are also great for improving your balance and coordination over time.

That said, the ultimate goal of this plank variation is “anti-rotation and full stabilization of your entire core,” Borden says.

“It’s not so much what you are doing with your hands and shoulders—it’s about what’s not moving,” explains Clancy. “The move is more challenging than a traditional plank because it requires much more core awareness.”

By keeping your core and lower half completely still as you perform this move, you are improving your ability to control those areas of the body and training your mind to reconnect with those specific muscle groups. This is a concept called mind-muscle connection, and it’s based on the idea that by simply concentrating on how your muscles are engaged during an exercise, you can help them work more efficiently.

“The more control you have over your body, the less likely you are to injure it,” Clancy adds.

Another big plus of shoulder taps: You can do them anywhere, without any equipment.

Here’s how to do the move:

Start in a high plank with your feet slightly wider than hip-width apart, hands under your shoulders, and your core, glutes, and quads engaged.

Without moving your hips up and down or side to side, lift your right arm and tap your right shoulder with your hand.

Lower, switch sides, and repeat for 1 rep.

Do 10 reps.

To help clients master proper form, Borden tells them to visualize a cup of coffee on their lower back while doing the move. “Sometimes I will put a shoe or something light on my client's lower back so they can feel if they are moving their hips around too much during the exercise,” she adds. You can also move your feet a little further apart for some extra balance help.

If you’re new to planking, try modifying the move by just tapping your opposite hand, rather than reaching all the way up to your shoulder. Another modification is to keep both hands planted on the ground, but shift 80 to 90 percent of your body weight from arm to arm for 1 to 2 seconds at a time.